Bottom Line:
Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature.An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis.Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

ABSTRACTQuiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

Figure 7: Maintenance of pEC-associated ATPDase activity by antioxidants after TNFα stimulation. Superoxide dismutase (SOD; Cu-Zn form, 330 U/ml); the hydrogen peroxide scavenger catalase (1,000 U/ml) and the 21-aminosteroid des-methyl tirilazad (U74389; final concentration 5 μM) were again used as antioxidants. Such interventions could protect against the statistically significant TNFα-mediated inhibitory changes in pEC ATPDase activity, and had minimal positive effects on quiescent pEC ATPDase levels. Inhibition of ATPDase activity following TNFα activation was consistently abrogated by these antioxidants (data are expressed as mean and standard deviations).

Mentions:
We next evaluated whether effective combinations of superoxide dismutase (SOD) and catalase, or more novel antioxidants such as 21-amino-steroids (des-methyl tirilazad) could protect EC against TNFα-mediated changes in ATPDase activity in vitro. The inhibition of ATPDase activity following TNFα activation was consistently abrogated by the selected antioxidants (Fig. 7). SOD and catalase were also able to preserve pEC ATPDase activity following the addition of the exogenous oxidant systems (Fig. 6 a).

Figure 7: Maintenance of pEC-associated ATPDase activity by antioxidants after TNFα stimulation. Superoxide dismutase (SOD; Cu-Zn form, 330 U/ml); the hydrogen peroxide scavenger catalase (1,000 U/ml) and the 21-aminosteroid des-methyl tirilazad (U74389; final concentration 5 μM) were again used as antioxidants. Such interventions could protect against the statistically significant TNFα-mediated inhibitory changes in pEC ATPDase activity, and had minimal positive effects on quiescent pEC ATPDase levels. Inhibition of ATPDase activity following TNFα activation was consistently abrogated by these antioxidants (data are expressed as mean and standard deviations).

Mentions:
We next evaluated whether effective combinations of superoxide dismutase (SOD) and catalase, or more novel antioxidants such as 21-amino-steroids (des-methyl tirilazad) could protect EC against TNFα-mediated changes in ATPDase activity in vitro. The inhibition of ATPDase activity following TNFα activation was consistently abrogated by the selected antioxidants (Fig. 7). SOD and catalase were also able to preserve pEC ATPDase activity following the addition of the exogenous oxidant systems (Fig. 6 a).

Bottom Line:
Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature.An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis.Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

ABSTRACTQuiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.